Primary Hyperoxaluria (PH) is a rare genetic disorder that results from an excessive endogenous synthesis of oxalate. Glyoxylate reductase is a key enzyme in this biosynthetic pathway for converting glyoxylate to glycolate and limiting its conversion to oxalate. In Type 1 PH, its activity results in an excessive production of glycolate, which is excreted in urine. In Type 2 PH, its absence leads directly to an increased conversion of glyoxylate to oxalate. The long-term goals of this research are to better define the pathways leading to glyoxylate production and oxalate synthesis in PH, and to use this information to develop therapies to treat the disease. The hypothesis to be tested is that hydroxyproline metabolism is a major source of glyoxylate production. Two specific aims have been developed to test this hypothesis. In the first, the metabolism of labeled hydroxyproline will be examined in normal individuals and those with PH. These studies will be conducted in the Clinical Research Center using carefully controlled diets and by obtaining blood and urine samples to monitor hydroxyproline metabolism. In the second, cell models will be developed that are deficient in GR activity, to elucidate the consequences of GR deficiency in several different types of tissues. GR deficiency will be created by modifying gene expression using RNA silencing techniques. The metabolism of hydroxyproline to oxalate will be examined in vitro under controlled conditions and ways to reduce it will be investigated. These studies will increase our understanding of the metabolism associated with oxalate synthesis and will identify new therapeutic strategies to decrease it.